The present invention relates to a novel drainage method and the strap draining materials therefor and, in particular, to a draining method adapted for use in drainage system in the soil conservation on mountain slopes, agricultural industry and in civil engineering work and to flexible thin sheet like draining straps having a high resistance to pressure and a high efficiency of drain absorption.
Conventionally, the most frequent use of water permeable and draining materials in drainage in the soil conservation on mountain slopes, underground irrigation and drainage on farms, and the civil engineering work on tunnel road bases and retaining walls are of a tubular type, that is, the so-called permeability pipes or drain pipes. The basic structure of a drain pipe is all that the circumference of at least of more than a half of the upper half portion of the circular tubular pipe is opened up with numerous tiny cracks densely distributed like meshes of a net for collecting infiltration water from the soil cover into the non-porous water collecting part of the lower half portion in the pipe and from there again water to flow out along the longitudinal direction of the pipe. However, because the infiltration water moves water to flow downwardly into the lower half portion of the pipe by the water head and the water gravity, it must also carry along the tiny sandy particles into the meshes. Certainly, the sandy particles after collecting for some time gradually seal the meshes resulting thus in a blockade. Even though a part of the sandy particles entering the pipe can be discharged together with the water that has infiltrated into the pipe, because the amount of water collecting in the pipe is small and the speed of drain flow is low, a majority of sandy particles will settle on the lower half portion of the pipe. When collecting over a long period, it also results in disadvantages that there is blockade in the pipe and reduction in the amount of drain. Sometimes, to prevent blocking of the meshes, there is covered on the outside of the drain pipe with a non-woven coating or a synthetic fiber gauze as the filtering layer thereby forming a multiple-layer permeability pipe or drain pipe.
However, since after use over a period of such a filtering layer blockade can still occur, its use would merely accomplish the effect of prolonging the life only. Furthermore, as drain pipes of the kind are mostly made of a hard plastics, this makes the construction process on embedding relatively inconvenient. Again, as the total area of the meshes provided on the unit area of the circumference of the drain pipe to act as the water inlet hole differs greatly from the pipe diameter sectional area (water service sectional area) and the actual amount of drainage in the drain pipes is less than one third of its sectional area, no siphonic action will thus be created. On the other hand, if the circumference of the pipe is formed densely with meshes, there will be a great reduction in the resistance to pressure in the drain pipe and the pipe can hardly be resistant to the soil pressure and the heavy pressure from vehicles, the drain pipe will get distorted easily and will even break by pressure leading to a blockade in the meshes or the pipe.
In order that the drain pipe be flexible and bendable to facilitate construction, a soft flexible permeable pipe made of various materials of PVC coated screw-type spring steel wire, non-woven fabric tube and nylon yarn has also been disclosed. However, even with such a flexible permeable pipe the problems of the aforesaid blockade in the meshes and the resistance to pressure still remain.
Others also include disclosure of forming a screw ditch on the outer circumference of a hard plastic drain pipe and in which the meshes are provided inside the ditch whereby it enhances the strength of the pipe body and improves the absorption efficiency.
There is disclosed also another type of a non-tubular type of drain sheet. This type of drain strap is formed by coating on the surface of a hard plastics formed concavo-convex support body with a layer of felt non-woven fabric. The support body also has the two sides formed in ditches, however, the opening of the ditches is broader than the ditch bottom.
It is the purpose of the present invention to provide a new draining material which differs in construction, shape and principle from the foregoing various drain pipes and sheets, and which possesses a large drainage of high absorption rate, a resistance to pressure and is without a blockade and further is adapted for use in all kinds of drainage system.